Question

cordaitales is unique among the gymnosperm "justify the statement "​

Answer 1

(1) The members of Cordaitales were tall and slender trees, the trunks often reaching a height of 10-30 metres before branching. The long slender shaft bore a dense crown of branches, on which were produced an abundance of large and simple leaves. No such habit is known among the existing gymnosperms.

(2) The vascular cylinder is collateral and endarch. The tracheids are thick-walled and compactly arranged. The radial walls are heavily pitted and the pits are alternately and multi-serially arranged. The pits are segregated into groups with unfitted spaces which are the characteristic of the group. This is not found in any other group, living or fossil. The innermost wood forms a ring of separate xylem strands. Double leaf trace is present. Pith is large and separate.

(3) The leaf is very variable in shape, rounded to very slender in size. No midrib is present, but a series of parallel lines traverse the length of the blade. They were borne on spiral sequence on the smaller branches that formed the crown of the tree. The bundles were surrounded by bundle sheath and connected by transverse bridge of thick-walled cells.

(b) Spore-Producing Organs:

(1) Fructifications are lax inflorescences on the slender stems among the leaves.

(2) The strobili of the male inflorescence contain 1-6 or more fertile bracts (microsporophylls), each of which supports as many as 6 terminal elongated pollen sacs.

(3) Each female strobilus usually contains 1-4 ovuliferous appendages (megasporophylls). In some cases, megasporophylls are forked and bear two terminal flattened ovules.

(4) Air sacs rendered the pollen buoyant and facilitated easy dispersal by wind.

(5) The winged seeds are flattened and heart-shaped, the nucellus is free from the integument except at the base and the vas­cular supply is double. The nucellar beak of the pollen chamber projects into the micropyle. Fertilization probably took place by swimming sperms. If a pollen tube was present, it probably func­tioned as an absorptive organ as in recent Cycads and Ginkgos.